Signaling system



F. R. BRIDGES SIGNALING SYSTEM Oct. 6, 1936.

Filed Jul 2, 1932 s Sheets-Sheet 1 Oct. 6, 1936. F. R. BRIDGES S IGNALING SYSTEM 3 Sheets-Sheet 2 63105 X ling- Filed July' 2, 1932 w egg 3 Oct. 6, 1936. F. R. BRIDGES 2,056,709

SIGNALING SYSTEM Filed July 2, 1932' 3 Sheets-Sheet 3 Patented Oct. 6, 1936 UNITED STATES,

SIGNALING SYSTEM Frank R. Bridges, Needham, Mass., assignor to The Gamewell Company, Newton Upper Falls, Mass, a corporation of Massachusetts Application July 2, 1932, Serial No. 620,683

16 Claims.

emergency signaling, but provides improvements which render the operation of signaling systems of this type especially secure and certain.

The primary object of the present invention is to provide a signaling system with an emergency conductor which, under faulty conditions of the system, is supplied with current independently of the normal current supply, the circuit being so arranged that the current for emergency operation is not influenced by the nature of the existing fault, so that the emergency operation'is independent ofany abnormal conditions which might influence an emergency current source which is in any manner dependent upon, or associated with the normal current source and the normal operation of the system generally.

Other objects are to provide a signaling system using direct current for normal operation and alternating current for emergency operation, or conversely, the efiectiveness of the emergency current being independent of the normal current and the nature of the faulty condition which necessitates emergency operation, to provide a signaling system employing normal line current for emergency operation, to provide an unweakened and undistorted alternating current supply for signaling under all emergency conditions, and to provide an emergency power source for a signaling system of the nature referred to whose characteristics, as, for example, the voltage, can be adjusted to conform with prevailing conditions (especially the ground resistance of a given a circuit), independently of circuit characteristics which influence the character of the current for normal operation.

A further object is to provide a signaling system employing two distinct current supply and signal reception circuits, one carrying alternating current and the other direct current, and two partly identical signal transmission circuits as, for example, normal and emergency transmission circuits, whereby each supply circuit is exclusively associated with one of the two transmission circuits.

Still further objects .are to provide an improved signaling system with emergency conductor, which permits the installation of simple and effective provisions for connecting reserve power supply means in case of failure of the normal power supply, and to provide a power supply arrangement with provisions of this kind.

In one aspect, the invention provides in its 1 preferred embodiment a signaling system with a normally closed signal line or loop continuously energized with direct current, and an alternating current source also continuously associated with the circuit and in addition with an emergency conductor, usually the ground, permitting the transmission of signals over the latter, and that portion of the normal circuit which remains serviceable. The invention also provides means which keep the two current sources electrically separated, thereby preventing any unfavorable mutual influence. This arrangement permits emergency operation, for example, with current derived from an ordinary public utility line, uninfluenced by any connection with the normal source of signaling current and, in one modification, the constant flow of superposed alternating and direct currents in the outside signal circuit. Normal operation takes place only with direct current acting upon certain signal manifesting devices, whereas alternating current is employed for emergency operation with a different set of manifesting devices. This provides for the possibility of independent adjustment to certain problems which are different for normal and emergency signaling as, for instance, adjustment to impedances which may be quite distinct in both cases. The usefulness of previous systems operating through emergency ground connections is limited mainly by the relatively high resistance of the ground connections. To maintain sufiicient current flow through these connections requires voltages which are under normal circuit conditions excessive. By providing two separate current supply sources, one for ex- 3 ample a direct current source of a voltage only sufficiently large to maintain current fiow'through the normal circuit, and a second independent I source furnishing alternating current for emergency operation, I am enabled to choose an alternating current voltage sufi'iciently high to send a satisfactory signaling current through ground connections of relatively high resistance. The general advantages of having an emergency supply of full power not derived from a source which is also ne for normal signaling and which might be incfpacitated just when its proper operation is most desirable, that is, underemergency signaling conditions, are obvious.

As mentioned hereinbefore, the signal transmitting means used in my new circuit maybe of any well-known type, provided that they are not only adapted to send signals by interrupting the normal circuit, but also to establish connections to an emergency conductor (usually the ground) and to send signal impulses over this emergency connection. In order 'to avoid difilculties due to shunt paths under certain circuit conditions, heretofore known systems required special signal transmitting means which make connection to ground only in the event of circuit trouble. The present system does not require direct metallic connections to ground for emergency signaling, in order to' provide an emer gency signaling circuit of sufiiciently low resistance, but permits the use of alarm boxes which ground during each signaling period, whether the circuit is abnormal or not, by establishing ground connections which, however, are only effective for emergency signaling if the circuit is actually abnormal. Alarm boxes of this type operate more eifectively with full alternating emergency current than with fluctuating or more or less irregularly alternating emergency current of other systems which derive normal and emergency current from the same source.

As indicated above, the present invention contemplates, generally speaking, a source of current of a certain type, preferably direct current, either for each individual signal circuit, or for several circuits in multiple, and recording devices re- .sponding to this current which is employed for signaling under normal conditions. In addition a second, independent source of a different type of current, preferably ordinary alternating current, is provided for emergency signaling, this source being associated with the emergency conductor and cooperating with signal recorders responsive'to this second current. Means as, for example, choke coils and condensers, are further provided for electrically separating the two kinds -of supply sources and recorders, as will be described in detail hereinafter.

In another aspect, the new system permits the use of simple but eifective provisions for an emergency power supply in case the normal supply, as for instance the public utility system, fails. Since the normal and emergency signaling 55 sources are quite independent in their action,

any interlocking or otherwise correlating arrangements between normal and emergency current sources are unnecessary.

In a further aspect the new system is advantageous because existing signaling systems which have no provisions for signaling under the adverse conditions referred to above can be easily changed in'conformity with the present invention merelyby adding relatively simple and inexpensive parts, so that it is not necessary to discard existing equipment in order to take'advan tage of the improved arrangements of the invention.

Still further objects, aspects, and advantages of 70 the invention will be apparent from the following -",75 system incorporating the invention;

Fig. 2 is a similar diagram of a modified embodiment of the invention;

Figs. 3, 4 and 5 are simplified diagrams of a circuit according to Fig. 1 indicating the operation of the new system under various conditions Figs. 6, 7 and 8 are similar simplified diagrams of a circuit according'to Fig. 2;

Fig. 9 is a connection diagram of an embodiment utilizing direct current for emergency operation; and

Fig. 10 is a connection diagram of a fire alarm system acccording to the present invention, with several signaling circuits and a reserve power supply arrangement.

Referring to Fig. 1, L denotes a signal line or loop leading to station terminals I and 2 and containing a number of signal transmitters, herein referred to as alarm boxes M, N, P, R and S which normally keep the signal loop closed and the ground connections open. Busses DC supply direct current of suitable voltage derived from any convenient sourcejand leads 3 and l of the direct current circuit D connect terminals I and 2 to these busses. Lead 3 contains an inductance I0 intermediate terminal I and its direct current bus, and a signal recorder X is inserted in lead 4 between terminal 2 and the other direct current bus. Although the signal recorders are herein indicated as being of the tape imprinting type, it is understood that any signal manifesting device may be used instead. A battery B, in the nature of a so-called floating reserve power supply, may be connected across leads 3 and 4. Busses AC supply alternating current, preferably from the public utility line, to the primary II of a transformer T. One terminal I4 of the transformer secondary I2 is grounded, whereas the other terminal I5 leads to conductor I, which'is part of an alternating current circuit A including lead 5 connected to terminal I, a capacitance 2 I an inductance 23, recorders Z andY, an inductance 24, a capacitance 22 and lead 6 connecting to terminal 2. Inductances 22 and 24, in series with condensers H and 22, are provided for. the purpose of compensating the phase displacing eflect of the capacitances, in order to decrease as far as possible the impedance of the alternating current circuit.

The direct current derived from busses DC continuously supplies the signal loop L, so long as the latter is not interrupted by the code signal sending means of an alarm box, or by a break in the line. Condensers 2| and 22 prevent direct current from entering circuit A, whereas circuit D is protected from alternating current by choke coil I0 which is so dimensioned that its induc tance presents an alternating current resistance of a magnitude excluding for practical purposes the alternating current of A. It will be obvious to any one skilled in the art, that inductance II passes substantially only direct current and that capacitances 2I and 22 pass substantially only alternating current, so that the loop L may carry superposed direct current and alternating current, whereas alternating current is excluded from circuit D and direct current from circuit A. It is also apparent that in a circuitaccording to rent corresponding to the E. M. F. supplied by the entire secondary I2.

As pointed out hereinbefore, the alarm boxes aosopoe in the outer circuit or loop may be of any known type having provisions for forming signals in a normally closed circuit and also facilities for signaling through an emergency conductor, normally the ground. Fig. 1 shows schematically various types of alarm boxes M, N, P, R. and S, as representatives of such signal initiating means, and these-boxes will now be shortly described as far as their characteristics have a bearing on the operation of .the boxes in a circuit according to contacts GI, 62 and 63 actuated by a code wheel 9 68 in such a manner that under normal inoperative condition of the box contacts BI and 62 are closed, thereby completing the series signaling circuit, whereas upon operating the box allthree contacts 8!, 62 and 63 are connected when BI is lifted by one of the cams of wheel 68, and then again disconnected when 6| descends after having passed over the cam. The opening of all three contacts interrupts the closed circuitfor normal signaling, whereas the interconnection of all three contacts intermittently grounds the circuts for emergency signaling, each signal impulse comprising one grounding and one interruption of the normal circuit. A condenser 85 may be connected intermediate contact 63 and ground.

The alarm box N is representative of signal transmitters similar to those described in the patent to Frederick W. Cole for Successive noninterference signal box, No. 553,838, dated February 4, 1896. This mechanism comprises nor.-

mally closed contacts H for shunting'the box circuit at rest, contacts 15 and 1B for normal signaling, and a non-interference magnet 13 which controls contacts 19, windings 13 being connected across contact 1 I. The non-interference magnet of this box, like thenon-interference device of grounding switch l9 incident to the engagement therewith of the teeth of the code wheel 18.. The normally open contact '59 is operable by the box mechanism to establish ground connection. Con tacts l5 and 18 are for normal signaling when switch 19 is open. During emergency operation, that is, if the signaling loop should remain open a longer time than the longest break within any signaling period, contacts 19 are closed and each connecton between 15 and I8 is accompanied by a connection with ground over l9, whereas if I5 and it are disconnected the ground connection is also interrupted. Instead of employing contacts 15 and it, as shown, a contact arrangement similar to that of box M (contacts BI, 82 and 68) may be incorporated in a box of this type.

' Box P is somewhat similar to that disclosed in tacts 8|, normally closed signaling contacts 88,

88 and non-interference magnet in series across the box terminals, and normally open contacts 82, 83, adapted to connect the line to ground.

B th pairs of contacts may be operated by the code wheel 88 as shown. If one code wheel is used, an insulating block 81 is arranged intermediate levers 8 2 and 84, so that lever 82 can move independently of 84, if the latter is retained in raised position by pin 89 associated with the armature of non-interference magnet 85 in such a manner that 88 moves underneath 84 if the armature is deenergized. Normally code signals are sent by contacts 84 and 86 opening and closing in accordance with the code represented by theteethof wheel 88 whereas, if the line is interrupted due either to a break or the fact that another box is already signaling-magnet 85 is deenergized, its armature drops, andmoves pin 88 underneath lever 84, thereby preventing it from breaking contact at 88. In this case, lever 82 continuesto cooperate with the code wheel, so that signals can be despatched over ground and a portion of the normal'signaling circuit. Preferably, a condenser 89 is arranged in the ground connection.

The signal transmitter R has-a normally closed shunting switch 18 which opens when the box is pulled and remains open so longas the box movement is operative, namely, so long as the double code wheel 98 rotates, the latter comprising two identical'toothedportions on a common shaft and being adapted to actuate two sets of switch levers 96 and 9], 98 and 99 respectively, 96 and 91, and 98'and 99 respectively being intercon- I followers of leve'rs9l and 99 rest on cams 88 of the code wheel, which' keep them in elevated position, thereby connecting levers '98and 91 with contacts ill and 92, respectively, whereas levers 98 and'99 arelifted from contacts 93and 94. Pin 58 is associated with the armature of the non-interference magnet I88 and permits free movement of levers 98 and9'l, if the'noninter-.

ference magnet'was energized during the initial signaling period of the box, notwithstanding a: subsequent deenergization due to the opening of.

the signaling circuit at 9! and 92 or a subsequently'pulled box. A locking arrangementaccomplishing this result is, for example, described in the above-identified patent to F. W. Cole. If no current is flowing in the circuit due to previous pulling of another box or to some accident, and non-interference magnet I88 is therefore deenergized upon the opening of ill, the pin .58 moves underneath lever 91 and prevents its dropping and therefore the opening of the circuit at 9i and 92. Therefore,v if box R is pulled with the circuit in good condition, as shown in Fig. 1,

- the circuit remains closed over 98, 9|, I88, 92 and 91; i8 is opened, magnet I88 remains energized, pin 58 is out of the way, and the circuit is opened and closed at M and 92 when the follower of 91 drops in the interdental spaces of its code wheel, thereby initiating code signals. Shortly after contacts 9|, 96 and 92, 91, respectively, open, contacts 93, 98 and 94, 99, respectively, close, and establish a ground connection. The

ground connection at Cl and 99 is again interrupted shortly before contact is reestablished at 9| and 82. When box R is sending, and the line is interrupted, as, for example, due to a break in the line, or due to another box already operating, pin" prevents levers 9i and 91 from dropping and interrupting the circuit at 9! and 82, whereas levers 98 and 99 are independent of the non-interference magnet and establish ground connections at 93 and 94 every time the follower of 98 passes over the teeth of code wheel 90.

The alarm box 8 is of the type as described and claimed in the copending application of Clarence E. Beach for Signal apparatus, Serial No. 573,150, filed November 5, 1931, now Patent No. 2,018,656, and comprises a shunting switch ill normally closed, conjointly operating signal switches H2 actuated by a code wheel Ill, noninterference magnet H3 and a grounding switch I IS with three contacts as indicated in the drawings. Boxes of this type, as well as boxes of the type N ground the circuit only when emergency conditions prevail, and can therefore be directly grounded, whereas boxes of the types M and P are preferably grounded over condensers. Box R, although grounding during each signaling period, may or may not be provided with grounding condensers.

In the modification according to Fig. 2, only an alternating current supply, indicated by busses AC, is provided. Direct current for sup plying loop L with boxes M, N and P is derived from the alternating current busses by means of a rectifier bridge C comprising four terminals 3|,

nals 3| and 32, the transformer primary 4| is supplied from busses AC, and the leads 3, 4 of direct current circuit D are connected to terminals II and I4. Circuits D and L are otherwise similar to the corresponding parts of Fig. 1, as indicated by the use of like numerals in both figures. Busses AC also supply primary iioftransformer Q, and terminals 54 and of the secondary" are connected to conductors 5i and 51 of the alternating current circuit A. The transformer secondary has an intermediate terminal or tap ll, which is grounded. The alternating current circuit A and the direct current circuit D are again electrically separated by a choke coil I. and condensers ii, 22, respectively, and a floating reserve battery B and inductances I3, 24 are also provided in this embodiment.

In certain instances, for example if only existing direct, current equipment is to be utilized,

it may be desirable to employ direct current apparatus in circuit A. As indicated in Fig. 2, this may be accomplished by connecting direct current recorders, or relays U, V and W by means of rectifier bridges 6!, 6i and 1. Hence, in the embodiment of Fig. 2, the signaling system may cuit the new system operates as follows: Referring more particularly to Fig. 3, which is a simplified diagram of the circuit according to Fig. 1, if the line is wholly normal and none of the boxes are operated or pulled, no alternating current flows in any part of the circuit since only one terminal of secondary I2 is connected thereto. Direct current fiows in circuits D and L and is excluded from circuit A by condensers 2| and 22 as hereinbefore described. Recorder X is normally energized, whereas recorders Y and Z are deenergized and, upon operation of a box, signals are received at X, recorders Y and Z remaining inoperative. The non-interference arrangements of any type of box operate exactly as in a non-grounded system. However, if the boxes are of the type which keep the signaling circuit closed, but establish ground, and'signal over ground each time when the noninterference magnets are deenergized, upon a box being pulled (as for example boxes of type R, referring to the designations of Fig. l), the signals of two simultaneously sending boxes are received correctly. For example, if box III (assuming it to be of type R) is pulled first and box Hi2 somewhat later, the direct current signals of llll are received at X, whereas alternating current circuits a and b are established by box ll! and corresponding signals received at Y and Z. Box I02 signals over Y and Z while box Ill operates, whereas upon llll stopping and releasing the direct current circuit, bcx'lfl assumes control of the direct current circuit and its remaining signal impulses are also received at X. a

In the case of a broken circuit, as indicated at c of Fig. 4, the direct current is interrupted, recorder X drops its armature and becomes incapacitated, and, provided that the boxes of the circuit do not ground the same upon deenergization of their non-interference magnets (for example, if the boxes are of type P or R), substantially no current flows in the system. If the circuit should employ boxes which ground the line uponits deenergization, (as for example boxes of type N or S), as indicated in Fig. 4 at d of box I02, alternating current flows through circuit e. If pulled, a'box of this type interrupts the ground connection according to its code, and its signals are received at T as will be apparent from l'ig. 4. Similarly, a box pulled at the other side of break 0 signals over recorder Z; If several boxes are pulled on the same side of the break, there is no non-interference action and the signals received at X or Y will be mingled. However, if two boxes are pulled on different sides of the break, both 'send comprehensible signals, the signal of I" being, for example, received at Y over circuit e and the signal of I over circuit f at recorder Z.

Assuming now an accidentally grounded signal loop as indicated at g in Fig. 5, the direct current recorder or relay X remains energized, since the direct. current circuit h is not interrupted, but alternating current circuits i and It now being established in addition. recorders Y and Z are also energized and attracted, indicating the faulty condition of the circuit. Since the direct current circuit is normal, correct signals are received at X from all boxes just as if ground 9 was not pres ent.

If a short circuit exists across a signal box, for example, around b x I02 as indicated at m in Fig. 3," this box is not able to signal over the direct current circuit since it is by-passed with respect thereto, but its signals are correctly received at recorders Y and Z, since upon becoming deenergized, the boxes of type N, P, R, and S drop the armatures of their exclusively direct current responsive non-interference magnets and signal through ground over circuits a and b of Fig. 3. Boxes of type M also signal through ground, as will be obvious from Fig. 1. The remaining unshunted boxes are not influenced by the short circuit around box I02 and send their signals in normal, manner. used and, for example, box WI and short circuited box I02 are pulled simultaneously, the signals. of I02 are lost since IOI signals normally over ground, so that the signals become mingled at the alternating current recorders. With boxes of types N, R and S, however, which do not normally connect the loop to ground, both boxes IM and I02, if simultaneously pulled, transmit understandable signals, box IOI over relay X and box I 02 over the alternating currentrecorders.

A short circuit across the entire signaling loop, as indicated at n of Fig. 3, influences a circuit according to my new system as follows. Any one of the short circuited boxes is able to send signals over ground, which signals are received at X and/or Y. However, under this condition, two or more simultaneously pulled boxes produce mixed signals since the non-interference mechanisms of all short circuited boxes are incapacitated upon being deprived of their energizing direct current.

The modification according to Fig. 2, of which i Fig. 6 is a simplified diagram, carries under normal conditions, direct as well as alternating currents because the secondary 52 of transformer Q applies normally an E. M. F. to circuit A. Recorders V and W are therefore normally energized like the direct current recorder X, and upon operation of any box correct signals are received at X, V and W, provided the circuit is in normal condition. Recorder U, however, is normally deenergized, since no current flows from the transformer to ground, so long as the signal loop is ungrounded. In case two or more boxes operate simultaneously, the non-interference devices thereof operate in the normal manner and correct signals are received at recorder X.

In the caseof a broken circuit, as indicated at c of Fig. 7, the direct current circuit is interrupted, the non-interference magnets of the boxes deenergized, and box I02 for example, if pulled, op-

' capacitated by the break.

Assuming now that the signal circuit is grounded, as indicated at r of Fig. 8, the direct current If boxes of type M and P are circuit s is not disturbed and all boxes operate correctly and with all their non-interference features, the signals being recorded at X. In addition, recorder U is energized by the alternating current flowing from the line ground to terminal 40 of the transformer indicating the faulty condition of the line.

If a short circuit exists around a signal box as, for example, short circuit t around box I02 of Fig. 6, this box is excluded from the direct current circuit, whereas the normal direct current operation of X, by the other boxes, remains intact. The non-interference magnet of box I02 grounds the box as indicated with dotted lines in Fig. 6 and the box signals. over circuit u, the signals being received correctly at U. The alternating current signals could not be received at V or W, since these recorders are continuously energized so long as there is no break in the signal circuit. In case a short circuited box, as for instance box I 02, and another box, as for example box I04 are operating simultaneously, the signals of box I04 are correctly received at X and the signals of I02 at U.

If the entire signal loop is shunted out, as indicated at v of Fig. 6, signals from any one box will be received correctly at the alternating current relay U, as will now be apparent from the foregoing description, Whereas signals from any simultaneously pulled boxes can not be correctly received under these extremely unfavorable circumstances.

From the foregoing description of the operation of my new signaling system during the existence of the principal forms of faulty circuit conditions, for various types of boxes, its emergency operation during disturbances caused by combinations of these principal faults can be deducted without further detailed explanations.

In certain instances it may be desirable to employ alternating current for normal signaling, and direct current for emergency transmission. For this purpose, my new system can be modified ac-'- cording to Fig. 9. In this 'figure, L is again the condensers H6 and III and is connected to the other circuits at III and H2. The direct current circuit D, also connected across terminals I I I and I I2, comprises a battery I40 having one terminal grounded, whereas the other terminal is connected to a recorder I2I. In series across I II and H2 are two choke coils I24 and I25 and two recorders I22 and I23, the second terminal of recorder I2I being connected intermediate I22 and I23. From the preceding explanation, it will be apparent that; under normal conditions of the line, signalsare received at II5, whereas the direct current circuit is deenergized if the line is not grounded. When the loop is interrupted, for example, at y, the alternating current circuit is interrupted, but signals can be despatched over ground and one of receivers I22, I23, depending on which side of the break the signaling box is located. The operation of this modification under other faulty conditions will be apparent from the preceding detailed description of the modifications with emergency alternating current, and direct current for normal operation.

The new system is. especially .well adapted for use with simple and reliable provisions for a reserve power supply, aswill now be explained with reference to Fig. 10, which shows an arrangement comprising several signal loops. This installation has an alternating current supplyindicated by busses AC, and two outer circuits or loops L which are associated with direct current supply circuits D and alternating current supply circuits'A. The circuits L, D and A are similar to corresponding arrangements of Figs. 1 and 2, corresponding elements being'identified with like numerals, and need therefore no further explanation. Instead of recorders, relay magnets E are shown, which may for example be associated with suitable repeater circuits. The outer circuits L include signal transmitters IIII, I20, I30 and also signal receiving stations as, for example, firehouses, as indicated by bells F. The circuits D are supplied from busses AC through rectifier bridges K whereas circuits A are supplied from busses I3I through transformers I32, busses AC and I3I being connected by a normally closed switch I6 I. A reserve battery RB, maintained in charged condition by any suitable arrangement known for that purpose, is adapted to supply current to the motor I68 of an inverter I through normally open switch I62. The generator I69 of the inverter is connected to busses I3I through normally openswitch I63. Switches I6I, I62 and I63 are operated by magnets 1', I12 and I13 respectively, which are normally energized from busses AC. Switch I6I remains closed, and switches I62 and I63 are open, so long as busses =AC supply the installation, for example, from the public utility system. when the alternating current fails, switch I6I opens, and switches I62 and I63 close. Battery RB starts the inverter which now supplies'busses I3I with alternating equivalents which ifall current similar to that normally flowing in busses AC. The direct current circuits D are then energized by floating batteries B, and busses AC and I3I are separated by open switch I6 I so that the inverter can not feed energy into the alternating current supply system. Upon the return of the normal current supply, the inverter is again separatedfrom the battery and alternating current supply by switches I62 and I63, and busses AC and, I3I are connected by switch I6I.

It should be understood that the present dis closure is for the purpose of illustration only and that this invention includes all modifications and within the scope of the appended claims.

I claim:

1. A signaling system comprising a normally closed signal circuit with signal senders andconductive for alternating and direct currents, said senders having means for signaling through I ground, means for supplying direct current to said senders having means for signaling through ground, means for supplying direct current to said circuit, an alternating current signal receiver and a grounded alternating current source connected in series with said alternating current receiver with its terminals across said circuit, said alternating current source normally feeding alternating current to said circuit through said terminals, and in addition through ground if said circuit is grounded. v

3. A signaling system comprising a normally closed signal circuit with signal senders and conductive for alternating and direct currents, said senders having means for signaling through ground, a direct current source normally supplying said circuit, a conductor including a signal recorder across said circuit forming an auxiliary signaling circuit and including said senders, means for excluding direct current from said conductor and an independent alternating current source connected between said conductor and ground, for supplying said auxiliary circuit with alternating current upon grounding thereof.

4. A signaling system comprising a signaling .loop, means for supplying from a normalpreferred powersource direct current tosaid loop and means for supplying thereto alternating current superposed upon said direct current, a normally disconnected reserve power supply, and means for energizing said second supply means from said reserve power supply, upon failure of said normal source.

5. A signaling system comprising a signaling loop, a preferred normal source of alternating current, an emergency source of direct current, means including a unidirectional conductor for supplying unidirectional electromotive force from said normal source to said loop, means including a normaliyclosed switch for supplying alternating electromotive force from said normal source to said loop simultaneously with said unidirectional electromotive force, means for converting the direct current supply of said emergency source to emergency alternating electromotive force substantially similar to the alternating electromotive force of said normal source and means for supplying said emergency alternating electromotive force to said loop, and for opening said a loop and said senders, a. second circuit supplying alternating current to said loop and said senders and connected to said emergency conductor, signal manifesting means in each 01 said circuits for direct reception from said senders, and means for excluding alternating current from said first circuit and for excluding direct current from said second circuit.

7. A signaling system comprising a normally closed signal loop carrying direct current and including signal senders and direct current signal receiving means, an emergency conductor which may be connected to rtions 01' said loop for signal transmission th rethrough, an auxiliary conductor exclusive of said direct current receiving means, having alternating current receiving means associated therewith, and including portions of said emergency conductor, and means for supplying alternatingv current to an auxiliary circuit including for efl'ective signaling at least part of said signal senders and formed by said auxiliary conductor and part of said signaling loop.

8. A signaling system comprising a normally closed signal loop including signal senders, an emergency conductor which may be connected to portions of said loop for signal transmission therethrough, a source supplying direct current to said loop and said senders, an alternating current signal receiver, an auxiliary circuit exclusive of said direct current source associated with said signal loop, said emergency conductor and said alternating current receiver for transmitting signals from said senders, and an independent source supplying alternating current to said auxiliary circuit through said emergency conductor, said alternating current receiver and said independent source being located in a portion of said auxiliary circuit which carries only alternating current.

9. A signaling system comprising a normally closed signal loop including signal senders and receivers and carrying direct current, an emergency conductor which may be connected to portions of said loop for signal transmission therethrough, an auxiliary conductor adapted to be associated with said signal loop to form a circuit exclusive of said receivers but including said emergency conductor and at least one of said senders to transmit signals therefrom, an, alternating current receiver and an alternating current source associated with said circuit and said conductor, said source normally superposing alternating current upon said direct current and supplying alternating current to said conductor if the latter is through said emergency conductor associated with said loop.

10. A'signaling system comprising a normally closed signal loop carrying direct current and including signal senders capable of signaling through ground, and an independent alternating current circuit including a receiver and an alternating current source connected across, and normally supplying saidloop, said alternating current source being grounded at a point dividing the voltage of said source.

11. A signaling system comprising a normally closed signal loop conductive for direct and alter nating currents, serially including signal transmitting devices capable of signaling through ground and having two terminals, a direct current source, a signal recorder and an inductance rent source, a signal recorder and an inductance serially connected across said terminals, and an alternating current source and a signal recorder connected across said terminals through capacitances, a point of said alternating current source being grounded. Y .r"

13. A signaling system comprising a normally closed signal loop conductive for direct and alternating currentsgserially including signal transmitting devices capable of signaling through ground and having two terminals, a direct current source, a signal recorder and an inductance serially connected across said terminals, two ca-' pacitances and a signal recorder therebetween serially connected across said terminals, and an alternating current source having one terminal grounded and the other terminal connected intermediate said capacitances.

14. A signaling system comprising a normally closed signal loop conductive for direct and alterdirect current circuit substantially excluding alternating current therefrom.

15. A signaling system comprising a signal loop with signal senders in series therein, an emergency conductor which may be connected to portions of said loop for signal transmission therethrough, a circuit supplying direct current to said loop and said senders, a signal manifesting means in said circuit, a second circuit supplying alternating current to said loop and said emergency conductor, said second circuit being connected between a point of said loop and a point of said emergency conductor and including in series a transformer and a signal manifesting means, and means for excluding alternating current from said first circuit and for excluding direct current from said second circuit.

16. A signaling system comprising a normally closed signal loop conductive for direct and alternating currents, serially including signal transmitting devices capable of signaling through ground and having two terminals, a direct current source, a signal recorder and an inductance serially connected across said terminals, two capacitances serially connected across said terminals, an alternating current source having one terminal grounded and the other terminal connected intermediate said capacitances, and a signal recorder connected in series to said alternating current source and one of said capacitances between ground and one of said terminals.

FRANK R. BRIDGES.

should be read with this correcti-o CERTIFICATE OF CORRECTION. 8.

imam No. 2,056,709. October e, 1936.

FRANK R BRIDGES error appears ,in the printed specification of iring correction 'as follows: Page 6, first and that the said Letters Patent form to the It is hereby certified that the above numbered patent requ column, line 68, claim 1 for "on" readan;

n therein that the same may con record of the case in the Patent Office.

Signed and sealed this 29th day of December A. D. 1936 Henry Van Arsdale (Seal) .Acting Commissioner of Patents. 

